This invention relates to processes for preparing aminophosphonic acids.
This invention relates to a process for preparing aminophosphonic acids, such as N- phosphonomethylglycine, known also by its common name glyphosate. Glyphosate is a highly effective and commercially important phytotoxicant useful in controlling a large variety of weeds and crops. It is applied to the foliage of a very broad spectrum of perennial and annual grasses and broad-leafed plants to achieve the desired control. Industrial uses include control of weeds along roadsides, waterways, transmission lines, in storage areas, and in other nonagricultural areas. Usually glyphosate is formulated into herbicidal compositions in the form of its various salts which retain the anionic form of glyphosate in solution, preferably in water.
Amine phosphonomethylation to produce an aminophosphonic acid using formaldehyde and di- or trialkylphosphites has been shown in the literature, e.g., U.S. Pat. No. 5,041,628; Polish Patent Nos. 136,276 and 159,424. Such phosphonomethylation produces aminophosphonate esters that must be hydrolyzed to obtain the desired aminophosphonic acid. Prior approaches to hydrolyzing the esters have used an acid such as hydrochloric acid, or a base such as sodium hydroxide. A common problem with these types of hydrolysis is that under basic conditions N- alkylation of aminophosphonate often occurs. When hydrochloric acid is used for hydrolysis, alkyl chloride formation also occurs. The formation of such by-products decreases the yield of the desired aminophosphonic acid and requires more extensive separation of the aminophosphonic acid from the resulting reaction mixture.
An economically and technically better method for hydrolyzing aminophosphonate esters that proceeds with high conversion and selectivity to aminophosphonic acid and avoids by-product formation is therefore desirable.